Explore Shale

Stage 1 - Perforation

An electric current is sent by wire to a perferating (perf) gun. The charge shoots small holes through the casing, cement, and a short distance into the shale.

Stage 2 - Fracturing

Shale is compressed and must be fractured to extract natural gas. Fracking fluid is sent into the casing under high pressure and out of the perfs into the rock. This causes the shale layers to crack.

Stage 3 - Production

The newly created cracks create a pathway for the gas to enter the casing. A plug is inserted to prevent fracturing fluids from entering this zone while additional sections of the casing are
perforated and fracked. After all sections have been fracked, the plugs are drilled out and gas flows to the surface.

Residential Well

Municipal Well

In Pennsylvania, gas wells cannot be drilled within 500 feet of structures and private water supplies or within 300 feet of streams or wetlands. Waivers allow companies to drill inside of these limits with additional protective measures.

Residential water wells reach an average depth of about 200 feet, but occasionally can reach depths of more than 500 feet.

The direction of horizontal drilling follows the natural fractures of shale rock.

A typical Marcellus Shale well is drilled 5,000 to 9,000 feet vertically and up to 10,000 feet horizontally.

About 37% of U.S. public water supply comes from groundwater sources, while the rest comes from surface water bodies like lakes, rivers, and reservoirs. Municipal wells work like residential wells, but typically have a larger diameter and higher flow rate.

Well casing is steel pipe that is inserted into a drilled section of a borehole and cemented in place.

As the borehole gets drilled deeper, smaller diameter casing sections are inserted within the previous casing.

Pennsylvania regulations indicate that casing must be cemented with an ASTM-approved cement to a minimum of 50 feet deeper than the deepest fresh groundwater.

The cement is intended to isolate the casing from groundwater and prevent natural gas from leaking up around the outside of the pipe, a condition that can potentially allow gas to enter the groundwater supply or cause gas to escape at the surface.

Why is water used in fracking?

In order to extract natural gas from low permeability shale, fracturing fluids are pumped into a wellbore, a process which increases pressure underground, causes shale layers to crack, and allows the gas contained within the shale to escape.

Water is accessible, affordable, and incompressible so it is the primary component of fracking fluid.

Roughly 72% of the water used for Marcellus Shale drilling comes from rivers, creeks, lakes, and groundwater in Pennsylvania. The other 28% is purchased from municipalities by drilling companies, removed from abandoned mines, or collected from rainwater landing on the well pad. Water may be transported to the drill site by truck or through temporary pipelines installed underground.

There are more than 50 known chemicals that may be added to the water that is used for hydraulic fracturing. These chemicals generally represent less than 1% of the total composition of the fracking fluid. Such chemicals avert microorganism growth, prevent corrosion of metal pipes, and maintain fluid viscosity.

Flowback may be treated through a variety of methods.

Hauled off site for treatment and/or disposal in permitted deep injection wells.

Who regulates water usage?

The Pennsylvania Department of Environmental Protection (DEP), in cooperation with the Delaware River Basin Commission and the Susquehanna River Basin Commission, regulates water used for Marcellus Shale drilling in Pennsylvania.

As part of the permit application process, drilling companies must identify the water sources from which they plan to obtain water and specify anticipated impacts. Sources may include rivers, streams, and lakes or municipalities and must be approved by the appropriate river basin commission.

DEP dictates that flowback must be treated to have a total dissolved solids (TDS) concentration of 500 parts per million or less for discharge into surface water bodies, which is consistent with Pennsylvania drinking water standards.

As of August 2011, there is currently only one facility in the statein Williamsportthat is capable of treating water according to this standard.

Methane migration: Naturally occurring methane may rise from its original home deep underground into upper levels of rock close to the surface. The methane may make its way into the groundwater supply and enter private wells drilled into the aquifer. The DEP has issued fines to gas companies for methane migration, although it is difficult to determine where the methane originated and whether it can be tied to Marcellus Shale drilling. Clearer cases of migration occur when methane rises up the space around the well casing due to faulty cementing procedures. This type of methane migration was documented by the DEP in at least 5 counties in 2011.

The Marcellus Shale lies underneath about 90,000 square miles of Pennsylvania, New York and West Virginia. It lies at varying depths from the surface to 9,000 feet and is believed to hold hundreds of trillions of cubic feet of natural gas, only a portion of which can be extracted with current technology. Between January and June of 2011, Marcellus wells produced 432.5 billion cubic feet of natural gas. During the same period in 2012, 895 billion cubic feet were extracted.

How did the Marcellus Shale form?

About 390 million years ago, what is now western Pennsylvania was part of a large inland sea. Biological matter and organisms dropped to this sea floor over time and mixed with sediments brought into the sea by rivers from the surrounding landmass. Over millions of years, as the continents moved and tectonic plates collided, mountains were formed, rivers were redirected, and the biological and inorganic sediments were buried under additional layers of rock, compressing them further. The extreme pressure and heat at greater depths converted the organic material into hydrocarbons, including those that make up natural gas. These hydrocarbons are not contained in reservoirs like oil, but rather are distributed throughout the shale in very thin layers and pores. This is why the rock must be fractured for the gas to escape.

How much land has been affected by Marcellus Shale drilling?

As of August 2012, about 6,400 Marcellus wells had been drilled in Pennsylvania and nearly 2,500 additional permits had been issued. On average there were two wells per pad, or roughly 3,200 pads in the state. Each pad (plus associated water impoundments, new roads, and other necessities) consumes between five and eight acres of land. This means that, as of 2012, Marcellus Shale drilling had affected approximately 20,800 acres of land, which is .07% of the total land area of the state.

About

About Marcellus Shale

The Marcellus Shale is a geologic formation of shale rock buried deep under parts of Pennsylvania, New York and West Virginia. This formation contains a large amount of natural gas distributed throughout the shale in cracks and pores.

Low-yield natural gas wells have been drilled in the Marcellus Shale for more than 50 years, but recent technological advancements in deep horizontal drilling combined with hydraulic fracturing techniques have exposed the possibility of more profitably tapping the shale for gas. The lure of profits has drawn numerous large drilling firms to the Marcellus region and spurred the leasing of thousands of acres of mineral rights from private citizens.

Part of the process of preparing a Marcellus gas well for production involves pumping millions of gallons of water, sand, and chemicals into the well under very high pressures to crack the shale apart and prop open the cracksa process called hydraulic fracturing, or “fracking.”

Mission

We develop and create public service media projects on a wide range of topics that stimulate dialogue around important social issues that impact people at both the local and national levels. Exploreshale.org enhances public understanding of the basic science surrounding the Marcellus Shale by providing a fact-based interactive learning experience.

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Explore Shale

Why is water used in fracking?

In order to extract natural gas from low permeability shale, fracturing fluids are pumped into a wellbore, a process which increases pressure underground, causes shale layers to crack, and allows the gas contained within the shale to escape.

Water is accessible, affordable, and incompressible so it is the primary component of fracking fluid.

How much water is used?

Each drill site requires between 3 and 5 million gallons of water per frack. Based on approximately 1,500 horizontal wells fracked in 2011, Pennsylvania used about 12-20 million gallons of water per day for Marcellus Shale drilling, which represents approximately .5-.8% of the 9.5 billion gallons of water the state uses daily.

Where does the water come from?

Roughly 72% of the water used for Marcellus Shale drilling comes from rivers, creeks, lakes, and groundwater in Pennsylvania. The other 28% is purchased from municipalities by drilling companies, removed from abandoned mines, or collected from rainwater landing on the well pad. Water may be transported to the drill site by truck or through temporary pipelines installed underground.

What is in fracking fluid?

There are more than 50 known chemicals that may be added to the water that is used for hydraulic fracturing. These chemicals generally represent less than 1% of the total composition of the fracking fluid. Such chemicals avert microorganism growth, prevent corrosion of metal pipes, and maintain fluid viscosity.

What happens to the water after it has been used for fracking?

Approximately 10% to 30% of the total water used per frack returns to the surface with the extracted gas. The remaining water remains deep underground. It is mostly absorbed by the shale formation, which is isolated from the water table.

Hauled off site for treatment and/or disposal in permitted deep injection wells.

Who regulates water usage?

The Pennsylvania Department of Environmental Protection (DEP), in cooperation with the Delaware River Basin Commission and the Susquehanna River Basin Commission, regulates water used for Marcellus Shale drilling in Pennsylvania.

As part of the permit application process, drilling companies must identify the water sources from which they plan to obtain water and specify anticipated impacts. Sources may include rivers, streams, and lakes or municipalities and must be approved by the appropriate river basin commission

DEP dictates that flowback must be treated to have a total dissolved solids (TDS) concentration of 500 parts per million or less for discharge into surface water bodies, which is consistent with Pennsylvania drinking water standards.

As of August 2011, there is currently only one facility in the statein Williamsportthat is capable of treating water according to this standard.

Methane migration: Naturally occurring methane may rise from its original home deep underground into upper levels of rock close to the surface. The methane may make its way into the groundwater supply and enter private wells drilled into the aquifer. The DEP has issued fines to gas companies for methane migration, although it is difficult to determine where the methane originated and whether it can be tied to Marcellus Shale drilling. Clearer cases of migration occur when methane rises up the space around the well casing due to faulty cementing procedures. This type of methane migration was documented by the DEP in at least 5 counties in 2011.

How large is the Marcellus Shale?

The Marcellus Shale lies underneath about 90,000 square miles of Pennsylvania, New York and West Virginia. It lies at varying depths from the surface to 9,000 feet and is believed to hold hundreds of trillions of cubic feet of natural gas, only a portion of which can be extracted with current technology. Between January and June of 2011, Marcellus wells produced 432.5 billion cubic feet of natural gas. During the same period in 2012, 895 billion cubic feet were extracted.

How did the Marcellus Shale form?

About 390 million years ago, what is now western Pennsylvania was part of a large inland sea. Biological matter and organisms dropped to this sea floor over time and mixed with sediments brought into the sea by rivers from the surrounding landmass. Over millions of years, as the continents moved and tectonic plates collided, mountains were formed, rivers were redirected, and the biological and inorganic sediments were buried under additional layers of rock, compressing them further. The extreme pressure and heat at greater depths converted the organic material into hydrocarbons, including those that make up natural gas. These hydrocarbons are not contained in reservoirs like oil, but rather are distributed throughout the shale in very thin layers and pores. This is why the rock must be fractured for the gas to escape.

How much land in Pennsylvania has been affected by Marcellus Shale drilling?

As of August 2012, about 6,400 Marcellus wells had been drilled in Pennsylvania and nearly 2,500 additional permits had been issued. On average there were two wells per pad, or roughly 3,200 pads in the state. Each pad (plus associated water impoundments, new roads, and other necessities) consumes between five and eight acres of land. This means that, as of 2012, Marcellus Shale drilling had affected approximately 20,800 acres of land, which is .07% of the total land area of the state.

More Information

In Pennsylvania, unconventional gas wells cannot be drilled within 500 feet of structures and private water supplies or within 300 feet of streams or wetlands. Waivers allow companies to drill inside of these limits with additional protective measures.

Drinking water wells reach an average depth of about 200 feet, but occasionally can reach depths of more than 500 feet.

About 37% of U.S. public water supply comes from groundwater sources, while the rest comes from surface water bodies like lakes, rivers, and reservoirs. Municipal wells work like residential wells, but typically have a larger diameter and higher flow rate.

Well casing is steel pipe that is inserted into a drilled section of a borehole and cemented in place. As the borehole gets drilled deeper, smaller diameter casing sections are inserted within the previous casing.

Pennsylvania regulations indicate that casing must be cemented with an ASTM-approved cement to a minimum of 50 feet deeper than the deepest fresh groundwater. The cement is intended to isolate the casing from groundwater and prevent natural gas from leaking up around the outside of the pipe, a condition that can potentially allow gas to enter the groundwater supply or cause gas to escape at the surface.

The direction of horizontal drills follows the natural fractures of shale rock.

A typical Marcellus Shale well is drilled 5,000 to 9,000 feet vertically and up to 10,000 feet horizontally.

Content updated August 2014.

Glossary

Shale

Shale is a dense, low permeability sedimentary rock. Shale differs from rocks of similar composition by breaking along thin layers that are less than one centimeter thick.

Water Table

The water table is the depth below which all of the pore spaces and cracks in rocks and sediments are completely saturated with water.

Hydraulic Fracturing

Hydraulic fracturing (fracking) is the process of injecting fluids under high pressure into a well to create fractures in deep shale rock that allow natural gas to escape.

Horizontal Drilling

Horizontal drilling is a process that sends a drill vertically underground up to 10,000 feet, then turns it at a 90-degree angle and drills horizontally several thousand more feet. On average, horizontal wells produce 3 to 5 times more natural gas than vertical ones.

Flowback

Flowback is fluid that returns to the surface with extracted gas. It may contain clay, salts, rock particles, naturally occurring elements dissolved from the rock, and chemicals that were added prior to beginning the hydraulic fracturing process. Most flowback occurs within 7-10 days of drilling, but may continue for 3-4 weeks. Flowback is captured in lined pits or metal tanks and must be treated and reused at another drill site or transported by truck or pipeline for proper disposal.

Slickwater

Slickwater is the combination of water and chemicals used in hydraulic fracturing to reduce friction, maintain pressure, and increase fluid flow into the well.

Proppant

Proppant is a porous material such as sand or ceramic beads used in hydraulic fracturing to ensure that newly created shale fractures remain open. A typical well uses between 3,000,000 and 5,000,000 pounds of proppants.

Best Management Practices (BMPs)

Best Management Practices is a term commonly used to describe water pollution control in relation to industrial wastewater, municipal sewage, stormwater, and wetlands.